Most of the improvement in agricultural crop yields has been through inputs: getting more fertilizer to the plant, decreasing weeds, spacing, reducing loss from pests and local environmental changes. But the next big engineering feat will be with the plant molecular pathways themselves, in particular, photosynthesis. The article refers to C3 and C4 plants. What are plant geneticists trying to accomplish

It changes the genetic makeup to produce more yielding plants.

Explanation:

Plant geneticists trying to produce a plant which used all the inputs efficiently  in order to produce higher yield with the use of low inputs. C3 plants are inefficient plants because they uses resources not efficiently while on the other hand, C4 plants are those which utilizes resources efficiently means more growth by using less inputs or high conversion power so we can say that the Plant geneticists produce a plant by changing their genetic makeup.

the offspring would all be white. if the parents are both white flowers then they have the genotype rr, which when crossed results in an all white punnet square.

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.